In the field of electronic testing and diagnosis of defects in circuit boards, it is necessary to effect electronic probe contact with components on the circuit board under test. One type of known testing technique makes use of the so-called "bed of nails" test fixture wherein an array of contact pins mounted through a perforated platform is arranged to contact a plated side of the circuit board. As shown, for example, in the German Offenlegunsschrift 2051052, an array of double-ended spring-loaded pins is positioned between the plated side of a board under test and a plurality of electrically conducting leads coupling the pins to an electronic test equipment.
One known alternative to the above-mentioned spring-loaded pins is an array of Euler column bending beam probes capable of exerting uniform contact pressure on the plated side of the board under test. A commerically available DC mode test fixture sold by the DIT-MCO International Corporation of Kansas City, Mo., makes use of a plurality of Euler column probes, each probe being electrically insulated from all others. However, as the operating speed of logic components increases, electronic testers must have the capability of testing circuit boards at higher frequencies.
The proper design of a high frequency test fixture which provides the interface between an electronic tester and a circuit board becomes critical to achieve reliable test results. Traditional test fixtures using straight or twisted pair wires connecting a bed of nails to the electronic test equipment may generate crosstalk, ground noise and ringing effects. These deleterious effects are most prevalent at high frequencies. Furthermore, the effective lead inductance associated with the wiring can become problematic during in-circuit testing. Using double-ended spring-loaded backdriving and ground pins in combination with a stripline board does not, of itself, reduce the inductance of the circuit formed by the pins and the boards.
My U.S. Pat. No. 4,574,236, issued on Mar. 4, 1986, entitled "High Frequency Test Fixture" and assigned to the assignee herein, discloses a high frequency test fixture which comprises a support body having first and second substantially parallel major surfaces and a double-ended probe held by the support body between the first and second major surfaces thereof. A first probing element is located on the first major surface of the support body and positioned proximate to one end of the double-ended probe. A second probing element is located on the second major surface of the support body and positioned proximate to the other end of the double-ended probe. In order to substantially reduce noise and decrease the effective lead inductance of the test fixture, a transmission loop is formed in the support body between the first and the second probing element. This test fixture clearly overcomes the above-mentioned high frequencies deleterious effects. Although such a fixture operates satisfactorily for its intended purpose, there still exists a need for a high frequency test fixture capable of achieving high test densities on circuit boards and semiconductor integrated circuits.